For many years the automotive industry has sought a remote control system which could be assembled into a motor vehicle at the factory and employed by the ultimate purchaser for controlling various functions of the motor vehicle from a handheld transmitter. Such systems were envisioned for operating the door locks and trunk latch so that a driver could lock the doors upon leaving the vehicle or unlock the doors as approaching the vehicle. In addition, it was anticipated that such remote control system should also operate the trunk latch so that a hand-held transmitter could be employed for the purpose of unlocking the trunk as the driver approached the vehicle for the purpose of facilitating loading of the trunk without the need for manipulating a key which can present difficulties and inconveniences when burdened with packages, at night when vision is hampered or when ice inhibits insertion of a standard key. Such remote control systems have been sought by the automobile industry for the purpose of either standard equipment or as an option; however, even though the concept appears quite susceptible to implementation, substantial problems have been encountered in efforts to develop such a successful remote control system. These difficulties have caused much interest in an approach which satisfies the demands of the automobile industry regarding price and lack of customer complaints.
The most prevalent concept to be employed for such a remote control system has been the use of a binary identification code which is transmitted from a transmitter by employing a modulated radio frequency signal having a coded portion that is indicative of an identification binary code. The binary code of such suggested system is fixed into the receiver and is outputted as a series of pulses of the radio frequency, which pulses have intelligence constituting the desired identification code. This binary identification code is fixedly contained in a receiving unit secured onto the motor vehicle, which receiving unit has a detector that allows passage of the particular radio frequency of the transmitter. Filters or other processing circuits convert the incoming coded signal into a replica of the binary code from the transmitter. This replica is compared to the identification code in the receiver and determines whether or not the coded portion of the transmitted signal matches the identification code stored in the receiver. Upon acknowledgement of a match between an incoming code portion of a received signal and the stored identification code in the receiver, the door lock is actuated. In accordance with this remote control concept, the identification code being transmitted to the receiver is accompanied by an appropriate function code of a binary nature, which function code is decoded upon matching of the identification code so that the desired function will be initiated by the receiver mounted in the motor vehicle. This desired function can be to lock the door, unlock the door or unlatch the trunk. Of course, other desired functions could be incorporated into the transmitted signal and identified by the receiver, such as activating the ignition system, initiating a security system, flashing the headlights, activating the horn, etc. to mention only some of the more obvious functions which could be controlled by the receiver upon identification of the proper incoming signal. Technology for accomplishing these various control functions is available. Many variations of this control theme have been suggested for controlling the door locks or the trunk latch of a motor vehicle.
Extensive effort to incorporate a remote control system, as explained above, as an OEM installation for motor vehicles has resulted in serious technical and practical impediments. Since the identification code in the receiver and transmitter must be functionally identical, the receiver and transmitter must be kept together during assembly of the vehicle. Since it is necessary that the receiver be mounted in an unaccessible, hidden position in the vehicle, the transmitter matched to the receiver must remain with the car as it is being assembled, painted, transported, displayed and sold. Should the transmitter be separated from the motor vehicle, the system is useless without some code arrangement maintained associated with the vehicle. A replacement transmitter would not have the same identification code as the factory mounted receiver. Consequently, the receiver would have to be disassembled, recoded, and matched with a new transmitter. The capability of accomplishing this goal is self-defeating, since the receiver now must be easily accessible and easily reprogrammed for a new identification code. The advantage of original equipment on the vehicle employing a remote control system is that the receiver can be assembled in the motor vehicle at a remote or hidden location so that disassembly and recoding is impossible. Only in this manner can the ultimate purchaser of the vehicle be assured that other persons do not gain access to the vehicle with another remote control transmitting unit. In addition, when a receiver is mounted at the factory, problems can be experienced when the hand-held transmitter unit is lost or misplaced. A new hand-held transmitter will not have the code of the receiver on the vehicle. One arrangement for solving this particular problem would be for the code of the receiver to be in some manner, maintained by the dealer or by the purchaser. Then, a manually manipulated coding arrangement could be imparted to anew transmitter for code matching purposes. To use this concept, the programming must be somewhat rudimentary and simple which defeats the intended security level of the system and destroys the basic objective of the original implementation of a factory assembled remote door lock control system. With the code being maintained by the dealer, security is compromised and record keeping must extend for the life of the vehicle. These factors are unacceptable.
Other difficulties have been experienced in matching receivers and transmitters employing binary transmitted codes. If a second transmitter is desired for use by another person, it must match to the transmitter originally supplied with the vehicle. To do this, the transmitter code must be read externally or again maintained by the dealer. A person finding the transmitter unit or gaining access to the dealer records could determine the code and prepare a duplicate without the car owner knowing that a duplicate transmitter exists.
As can be seen, the concept of mounting a receiving unit in the vehicle itself in an inaccessible location at the factory and also producing a security code concept which can not be manually duplicated by anyone having the original transmitter, another transmitter or access to dealer records presents serious problems. These problems have resulted in the inability of the automobile industry to develop a remote control system which is acceptable to the public and unobtrusive to the vehicle manufacturer with respect to code correlation and identification code security.